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A101953 Indices of primes in sequence defined by A(0) = 23, A(n) = 10*A(n-1) - 17 for n > 0. 1
0, 2, 6, 12, 23, 29, 47, 51, 162, 174, 218, 227, 260, 753, 950, 1343, 1572, 3293, 3522, 14160, 70793 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Numbers n such that (190*10^n + 17)/9 is prime.

Numbers n such that digit 2 followed by n >= 0 occurrences of digit 1 followed by digit 3 is prime.

Numbers corresponding to terms <= 950 are certified primes.

a(22) > 10^5. - Robert Price, Mar 04 2015

REFERENCES

Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.

LINKS

Table of n, a(n) for n=1..21.

Makoto Kamada, Prime numbers of the form 211...113.

Index entries for primes involving repunits.

FORMULA

a(n) = A102948(n) - 1.

EXAMPLE

2113 is prime, hence 2 is a term.

PROG

(PARI) a=23; for(n=0, 1500, if(isprime(a), print1(n, ", ")); a=10*a-17)

(PARI) for(n=0, 1500, if(isprime((190*10^n+17)/9), print1(n, ", ")))

CROSSREFS

Cf. A000533, A002275, A102948.

Sequence in context: A208850 A131520 A086953 * A084570 A069956 A062476

Adjacent sequences:  A101950 A101951 A101952 * A101954 A101955 A101956

KEYWORD

nonn,hard,more

AUTHOR

Klaus Brockhaus and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 23 2004

EXTENSIONS

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008

a(20)-a(21) from Robert Price, Mar 04 2015

STATUS

approved

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Last modified February 17 17:27 EST 2019. Contains 320222 sequences. (Running on oeis4.)